This invention relates to a linear matrix circuit, and more particularly to a linear matrix circuit having a conversion function by which matrix coefficients can be represented using a comparatively small number of parameters.
A television camera employs a circuit called linear matrix for filling up differences between chromaticity points of primary colors (RGB) prescribed in accordance with standards and chromaticity points of an actual camera. The circuit can be used to vary the color repeatability.
The circuit performs, for example, for a R signal, processing of multiplying difference components between the R signal and a G signal and difference components between the R signal and a B signal by coefficients and adding resulting sums and performs similar processing also for the G signal and the B signal. Where color signals before they pass the circuit are represented by R, G and B and the color signals after they pass the circuit are represented by Rxe2x80x2, Gxe2x80x2 and Bxe2x80x2, the color signals Rxe2x80x2, Gxe2x80x2 and Bxe2x80x2 can be represented by the following expressions:
Rxe2x80x2=R+xcex1(Rxe2x88x92G)+xcex2(Rxe2x88x92B)xe2x80x83xe2x80x83(1a)
Gxe2x80x2=G+xcex3(Gxe2x88x92R)+xcex4(Gxe2x88x92B)xe2x80x83xe2x80x83(1b)
Bxe2x80x2=B+xcex5(Bxe2x88x92R)+xcex6(Bxe2x88x92G)xe2x80x83xe2x80x83(1c)
where xcex1, xcex2, xcex3, xcex4, xcex5 and xcex6 are matrix coefficients.
Conventionally, if the circuit described above is used in order to obtain a color repeatability desired by its user, since it involves up to six matrix coefficients, it is very cumbersome to control the circuit. Further, the individual coefficients are mere coefficients on numerical expressions, and what are meant by them cannot be recognized personally. For example, it is difficult to imagine in what manner a color varies when the coefficient xcex1 is controlled.
The matrix circuit may employ another configuration wherein a color plane is divided into several portions and matrix coefficients are provided for the individual portions of the color plane. In particular, the configuration allows use of different matrix coefficients for the colors of red and blue.
As an example, eight axes which pass the origin are prepared on a color plane, and independent coefficients are provided individually on the axes. And, a color between two difference axes has a coefficient obtained by weighted meaning the colors of the axes in accordance with angles between the color and the axes. In this instance, since a coefficient does not exhibit a sudden variation depending upon the color, no unnatural color is exhibited.
However, with the circuit of the configuration just described, for example, where a color plane is divided into eight portions, up to 8xc3x976=48 coefficients must be controlled while they cannot be recognized personally. Thus, it is almost impossible to control the circuit in a manner desired by a human being.
On the other hand, in order to control the color of a video signal, a method is employed frequently wherein the video signal is represented by a brightness signal Y and two color difference signals R-Y and B-Y and the chromaticity is calculated by processing of the two color difference signals. With the method just described, however, where it is applied to an apparatus such as a television camera which handles primary colors, it is necessary to convert the primary color signals into color difference signals and then convert the color difference signals back into primary color signals. This gives rise to deterioration of the signals and enlargement of the circuit scale.
As described above, since the conventional linear matrix circuit for color conversion has a large number of matrix coefficients, it has a problem in that control thereof does not conform to a feeling of a human being and is cumbersome. Further, where a video signal is represented by and processed in the form of a bright signal and two color difference signals, conversion between the signals must be repeated. Consequently, the conventional linear matrix circuit has a problem in that repetition of such conversion gives rise to deterioration of signals and enlargement of the circuit scale.
It is an object of the present invention to provide a linear matrix circuit which can control linear conversion of color reproduction with a comparatively small number of parameters, which conform with a feeling of a human being, by means of a circuit of a comparatively small scale or software of a small scale using a comparatively simple method.
In order to attain the object described above, according to the first aspect of the present invention, there is provided a linear matrix circuit for linear conversion of color reproduction for use with an image processing apparatus which separates a video signal into three primary color components of red, green and blue and performs processing on each of the components, comprising coefficient conversion means for introducing six coefficients required for the linear conversion of color reproduction from two control parameters.
According to the second aspect of the present invention, with the linear matrix circuit, linear conversion of color reproduction can be controlled with two parameters by means of a circuit of a comparatively small scale or software of a small scale using a comparatively simple method.
The two control parameters may correspond to a saturation and a hue. With the linear matrix circuit, linear conversion of color reproduction can be controlled with the two parameters, which conform with a feeling of a human being, by means of a circuit of a comparatively small scale or software of a small scale using a comparatively simple method.
According to the third aspect of the present invention, where the three primary color components before the linear conversion are represented by R, G and B and the three primary color components after the linear conversion are represented by Rxe2x80x2, Gxe2x80x2 and Bxe2x80x2, matrix coefficients xcex1, xcex2, xcex3, xcex4, xcex5 and xcex6 before the linear conversion represented by
Rxe2x80x2=R+xcex1(Rxe2x88x92G)+xcex2(Rxe2x88x92B)
Gxe2x80x2=G+xcex3(Gxe2x88x92R)+xcex4(Gxe2x88x92B)
Bxe2x80x2=B+xcex5(Bxe2x88x92R)+xcex6(Bxe2x88x92G)
may be represented with a control parameter a for controlling the chromaticity and another control parameter b for controlling the hue by
xcex1=xe2x88x920.59axe2x88x920.59b
xcex2=xe2x88x920.11a+0.89b
xcex3=xe2x88x920.3a+0.2831b
xcex4=xe2x88x920.11axe2x88x920.4731b
xcex5=xe2x88x920.3axe2x88x920.7b
xcex6=xe2x88x920.59a+0.59b
With the linear matrix circuit, the coefficient conversion means can be implemented readily from a simple circuit or a simple program.